The present invention is related generally to multi-axis antenna arrangements and more particularly to an orthogonal multi-axis antenna arrangement in which the center of the overall antenna pattern is established with a relatively high degree of precision at a known point of intersection along two or three antenna axes. An associated method is disclosed.
Establishing the location of an electromagnetic signal source is important in a range of different applications including, but not limited to locating an underground boring tool using a locating signal which is transmitted from the boring tool. Generally, in such applications, antennas such as, for example, dipole antennas are used to measure the signal strength of the locating field along orthogonally opposed axes at one or more above ground locations. The measured signal strengths are then used to calculate the position of the boring tool. Unfortunately, however, locating applications which contemplate high levels of precision are typically limited by inaccurate signal strength measurements when prior art multi-axis antenna arrangements are used. The inaccuracy can be attributed to two significant sources: (1) it is inherently difficult to establish the origin/center of the antenna pattern of these prior art antenna arrangements in a very precise way and (2) particularly in the instance of a three axis orthogonal antenna arrangement, it is improbable that the three antenna axes actually intersect at one point such that electromagnetic field measurements taken by the arrangement actually represent, as nearly as possible, the electromagnetic field strength at a single point. In fact, when three dipole antennas are used, it is submitted that intersection of the three antenna axes at a single point which also comprises the center point of the antenna pattern of each of the dipoles is not possible.
The above incorporated U.S. application discloses a number of embodiments of a highly advantageous locating system for use in not only locating, but tracking an underground boring tool. In each of these embodiments, one or more above ground receivers include antenna clusters which are used to receive the dipole electromagnetic locating signal that is emanated from the underground location of the boring tool. In order to satisfy the need for an accurate orthogonal antenna, a highly advantageous cubic antenna arrangement is disclosed for use as the antenna cluster in the above ground receivers.
While the cubic antenna arrangement disclosed in the above incorporated application remains highly effective in solving the problems encountered in precision measurement of locating signal strength, the present invention discloses another highly advantageous and heretofore unseen antenna arrangement which also provides for precise measurement of a locating field at a single point and which further provides for remarkable ease of manufacture; high levels of manufacturing repeatability; highly stable, consistent performance; and reduced complexity in associated signal conditioning circuitry.